1. Field of the Invention
This invention relates to a processing unit for a substrate and a processing method for a substrate.
2. Disclosure of the Prior Art
Processes for manufacturing semiconductor devices include steps in which semiconductors as substrates undergo processes such as oxidation, diffusion, CVD (Chemical Vapor Deposition) or the like. Vertical thermal processing units are often used for conducting the various processes. A conventional vertical thermal processing unit comprises: a carrier-transferring area where an operator or an automatic conveying mechanism holds and conveys a carrier housing semiconductor wafers, and a loading area where semiconductor wafers in the carrier are transferred to a boat as a holder for a thermal processing which is then loaded into or unloaded from a thermal processing furnace.
In such vertical thermal processing units, it is preferable for a partition (bulkhead) to be provided between the carrier-transferring area which is exposed to the atmosphere and the loading area. The partition allows the loading area to remain clean and prevents a natural oxidation film from forming on the semiconductor wafers. The loading area should also be preferably filled with an inert gas such as nitrogen. A closed-type carrier, whose entrance for semiconductor wafers can be hermetically closed by a lid, should also be preferably used in the vertical thermal processing unit in order to prevent the semiconductor wafers from being contaminated with particles.
A carrier-placing portion having an opening is arranged at the partition between the carrier-transferring area and the loading area. The opening is adapted to become in contact with the carrier on the side of the carrier-transferring area. A door is provided at the opening on the side of the loading area to open and close it. When processing the semiconductor wafers, the lid of the carrier is aligned to be in contact with the carrier-placing portion, and the door and the lid are opened to communicate the interior of the carrier with the loading area. The semiconductor wafers are then conveyed from the interior of the carrier to the boat in the loading area via the opening. The boat is then loaded in the thermal processing furnace to perform the prescribed processes on the semiconductor wafers.
Furthermore, two boats are used as below. One boat of them is placed on the lid which can be vertically elevated to open and close the opening of the thermal processing furnace. The boat is conveyed into the thermal processing furnace. While the opening of the furnace is hermetically closed with the lid and the semiconductor wafers in the boat undergo the thermal processing, other the semiconductor wafers are transferred to the other boat. This improves the throughput of the vertical thermal processing unit.
Vertical thermal processing units for semiconductor wafers having large, for example 300 mm diameters need thermal processing furnaces having large capacities and large openings. Thus, after the thermal processing, considerable heat in the furnace may leak from the opening of the furnace into the loading area while the opening of the furnace is opened, the boat in the furnace is conveyed out, the next boat is conveyed into the furnace and the opening of the furnace is closed with the lid. This may raise the temperature of the loading area and influence instruments in the loading area. In addition, the wasted energy may be so much because the interior of the thermal processing furnace has to be maintained above the predetermined temperature.
The width, the depth and the height of the vertical thermal processing unit are increased accompanying the increase of the diameter of the semiconductor wafer, for example to 300 mm. The space of the floor and the height of the ceiling are also increased for arranging the vertical thermal processing unit. These lead to the increase of the costs for manufacturing and maintaining of the vertical thermal processing unit. Therefore, there is a requirement that the vertical thermal processing unit be miniaturized as much as possible.
In order to improve the ability to process the semiconductor wafers with the vertical thermal processing unit, it is desirable that the boat-placing portion is disposed in the loading area for placing one boat to which semiconductor wafers are transferred while the thermal processing is conducted to the other boat, that the transferring mechanism is disposed in the loading area for transferring the semiconductor wafers between the boat on the boat-placing portion and the carrier at the carrier-placing portion and that the boat-conveying mechanism is disposed in the loading area for conveying the boat between the boat-placing portion and the lid. Having the trace of the boat and the occupying space of the conveying mechanism overlap is effective in miniaturizing the vertical thermal processing unit. However, in that case, there is an undesirable possibility that the boat and the transferring mechanism interference with each other.
In addition, the boat before the thermal processing may be under the lee of the other boat after the thermal processing while the two boats are conveyed between the boat-placing portion and the lid respectively. In that case, the semiconductor wafers in the boat before the thermal processing may be contaminated with particles or gases coming from the other boat after the thermal processing.